The studies on the surface Ig functional capacities and tissue distribution of lymphocytes in the rabbit will be extended. The expression and distribution of surface Ig molecules on rabbit lymphocytes will be determined by immunoelectronmicroscopic labeling. Attempts will be made to identify parts of the IgG molecules on lymphocytes. In particular, the possible presence of VH or VL in the absence of other parts of the molecule will be examined. Cells bearing sIg of different immunoglobulin classes will be identified. Characterization of the cells with mixed T and B cell properties will be expanded. The role of different cell populations in induction of a PFC response will be determined and the role of the macrophage, if any, examined. The distribution of T and B cells in different lymphoid organs will be determined by immunoelectrophoresis.